1. Field of the Invention
The present invention relates to an internal combustion engine provided with a turbo-charger and a knocking control system. More particularly, it relates to a system capable of preventing an increase in the temperature of the exhaust gas.
2. Description of the Related Art
The temperature of the exhaust gas is determined by various engine operating conditions, such as the engine speed, load, and ignition timing. In particular, the exhaust gas temperature becomes extremely high when the engine speed or load is high. The temperature of the exhaust gas reaches a maximum value when the value of the air-fuel ratio of a combustible mixture is slightly higher than the theoretical air-fuel ratio when the engine speed, load and ignition timing values are constant. As the air-fuel ratio becomes lower than said value, i.e., the combustible mixture becomes richer, the temperature of the exhaust gas is further reduced.
When the temperature of the exhaust gas is increased, the catalytic converter is prematurely damaged. Therefore, a system has been proposed for realizing an enrichment correction of an injected fuel amount so that the air-fuel ratio is smaller than the theoretical air-fuel ratio (rich air-fuel mixture) when the engine is operated under a high engine speed or load condition. This fuel enrichment correction, however, causes a decrease in the fuel consumption efficiency, and further, the exhaust gas reaches a high temperature very shortly after the engine has entered the high speed or load condition. Therefore, usually an enrichment correction is not made until after a certain delay time has elapsed.
The delay time can be determined in accordance with the engine speed and load, as disclosed in Japanese Unexamined Patent Publication No. 58-51241. Alternatively, the delay time can be determined in accordance with the rate of change in the load increase, as disclosed in Japanese Unexamined Patent Publication No. 60-53645. The delay time also may be determined in accordance with the temperature of the cooling water of the engine.
The above mentioned solutions are sufficient for a conventional type of internal combustion engine, but when the engine is provided with a turbo-charger and a knocking control system using an ignition retard control, the prior art methods cannot effectively control the increase in the exhaust gas temperature.